serializing Grape::Entity::Exposure::NestingExposure::OutputBuilder fails in 0.7.0

When attempting to serialize a Grape::Entity::Exposure::NestingExposure::OutputBuilder in 0.7.0 using Marshal.dump (for caching), we encounter an error like TypeError: can't dump IO.

Rails.cache.fetch(key) do 
  present(entity_items).as_json   # this used to just give a Hash which could be marshaled properly
end

This error seems to stem from the options hash in the entity. When it contains the request environment (in the :env key), there are objects that cannot be marshaled.

In my testing (in development mode) the following keys contain unmarshalable items.

opts[:env].reject {|k,v| Marshal.dump(v) rescue false }.keys
["rack.errors",
 "puma.socket",
 "rack.hijack",
 "puma.config",
 "action_dispatch.logger",
 "action_dispatch.backtrace_cleaner",
 "action_dispatch.routes",
 "action_dispatch.remote_ip",
 "rack.session",
 "rack.session.options",
 "warden",
 "grape.routing_args",
 "api.endpoint"]

Start by reproducing the failure with Marshal.dump around the Rails.cache.fetch example, then inspect how the entity options hash carries opts[:env]. Use the listed unmarshalable environment keys to narrow the cause; done means the entity can be serialized for caching without the TypeError while retaining the expected output.